The procedure for FEA is very similar to the FEA procedure in Samarium. Multirun and thermal analysis are disabled. Cobalt automatically uses the peak current determined by the LRC circuit solution. As deep saturation may occur, it is important to understand the options offered by Samarium to control the non-linear relationship between B and H. Most accurate results can be obtained when BH data is available for very high flux densities. These can either be obtained specially from the steel manufacturer or created by the user just for use by Cobalt.  All steel data presently available in the database are meant for use with Samarium and do not contain data with very high values of B (flux density).

BH curve for an electrical steel used for the stator lamination

The BH curve for CHP50A is shown with the corresponding values for relative permeability, mu_r, below. Different electrical steels have vastly different properties. It can be seen that the data is complete and mu_r approaches unity at the end of the provided data. The data points obtained from the manufacturer's data is shown as bullets. The smooth blue curve is the cubic spline and contains values for mu_r which are less than unity as B increases. Samarium automatically corrects for this during calculations. While this data is very useful for the design of electric motors, it does not contain enough information for magnetizing fixtures where the flux density is the stator steel may exceed 3 T.

Variation of mu_r with increase in B

Cobalt can use spline extrapolation. Here the slope of the curve is controlled when values beyond the available data are desired. Alternatively, this flag can be turned off. If this is turned off, any value of B beyond the maximum value available in the data will always return the value of mu at the maximum value of B.

Options available to handle steel saturation in Samarium (Iteration page in FEA properties)

If the data is insufficient, the user can specify values for the flux densities in both the lamination and hub steel where saturation occurs. The use saturation flag is to be turned on here. Any value desired that is to be obtained from data greater than the maximum value is linearly extrapolated. The value of mu_r is unity at the specified flux densities.

Warning:

Unlike the operation of motors where only light saturation is likely, the operation of the magnetizing fixture during peak current drives the steel into deep or very deep saturation. So great care must be taken to ensure the quality of the BH data fed into the FEA engine.

When spline extrapolation is turned off or when saturation is used, the iteration may get "stuck" in periodic reductions in error and sudden increase. This can be observed in the Newton histogram of the FEA status dialog. When this occurs, it is the user's responsibility to alter the relaxation parameter ('q') available in the Iterations page of FEA properties to lower levels (0.5, 0.3, etc.). It is advised to start with the default value of zero.  This problem will be corrected at a later stage and is a result of insufficient steel BH data being available. These kind of problems will not occur if proper steel data is available and used without spline extrapolation. Some amount of experimenting will be required before identifying the best option to use based on the available steel BH data.